drm/atomic: Refcounting for plane_state->fb

So my original plan was that the drm core refcounts framebuffers like
with the legacy ioctls. But that doesn't work for a bunch of reasons:

- State objects might live longer than until the next fb change
  happens for a plane. For example delayed cleanup work only happens
  _after_ the pageflip ioctl has completed. So this definitely doesn't
  work without the plane state holding its own references.

- The other issue is transition from legacy to atomic implementations,
  where the driver works under a mix of both worlds. Which means
  legacy paths might not properly update the ->fb pointer under
  plane->state->fb. Which is a bit a problem when then someone comes
  around and _does_ try to clean it up when it's long gone.

The second issue is just a bit a transition bug, since drivers should
update plane->state->fb in all the paths that aren't converted yet.
But a bit more robustness for the transition can't hurt - we pull
similar tricks with cleaning up the old fb in the transitional helpers
already.

The pattern for drivers that transition is

	if (plane->state)
		drm_atomic_set_fb_for_plane(plane->state, plane->fb);

inserted after the fb update has logically completed at the end of
->set_config (or ->set_base/mode_set if using the crtc helpers),
->page_flip, ->update_plane or any other entry point which updates
plane->fb.

v2: Update kerneldoc - copypasta fail.

v3: Fix spelling in the commit message (Sean).

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

1 files changed, 7 insertions, 7 deletions

diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c
index fa56bb5da6c3..d99c452b0563 100644
--- a/drivers/gpu/drm/drm_plane_helper.c
+++ b/drivers/gpu/drm/drm_plane_helper.c
@@ -27,7 +27,9 @@
 #include <drm/drmP.h>
 #include <drm/drm_plane_helper.h>
 #include <drm/drm_rect.h>
+#include <drm/drm_atomic.h>
 #include <drm/drm_crtc_helper.h>
+#include <drm/drm_atomic_helper.h>
 
 #define SUBPIXEL_MASK 0xffff
 
@@ -464,7 +466,7 @@ out:
 		if (plane->funcs->atomic_destroy_state)
 			plane->funcs->atomic_destroy_state(plane, plane_state);
 		else
-			kfree(plane_state);
+			drm_atomic_helper_plane_destroy_state(plane, plane_state);
 	}
 
 	return ret;
@@ -505,15 +507,14 @@ int drm_plane_helper_update(struct drm_plane *plane, struct drm_crtc *crtc,
 	if (plane->funcs->atomic_duplicate_state)
 		plane_state = plane->funcs->atomic_duplicate_state(plane);
 	else if (plane->state)
-		plane_state = kmemdup(plane->state, sizeof(*plane_state),
-				      GFP_KERNEL);
+		plane_state = drm_atomic_helper_plane_duplicate_state(plane);
 	else
 		plane_state = kzalloc(sizeof(*plane_state), GFP_KERNEL);
 	if (!plane_state)
 		return -ENOMEM;
 
 	plane_state->crtc = crtc;
-	plane_state->fb = fb;
+	drm_atomic_set_fb_for_plane(plane_state, fb);
 	plane_state->crtc_x = crtc_x;
 	plane_state->crtc_y = crtc_y;
 	plane_state->crtc_h = crtc_h;
@@ -552,15 +553,14 @@ int drm_plane_helper_disable(struct drm_plane *plane)
 	if (plane->funcs->atomic_duplicate_state)
 		plane_state = plane->funcs->atomic_duplicate_state(plane);
 	else if (plane->state)
-		plane_state = kmemdup(plane->state, sizeof(*plane_state),
-				      GFP_KERNEL);
+		plane_state = drm_atomic_helper_plane_duplicate_state(plane);
 	else
 		plane_state = kzalloc(sizeof(*plane_state), GFP_KERNEL);
 	if (!plane_state)
 		return -ENOMEM;
 
 	plane_state->crtc = NULL;
-	plane_state->fb = NULL;
+	drm_atomic_set_fb_for_plane(plane_state, NULL);
 
 	return drm_plane_helper_commit(plane, plane_state, plane->fb);
 }